The present invention relates to a recording/reproducing apparatus, and method for recording or reproducing information in or from a recordable and reproducible medium by a head, particularly to a disk drive for recording or reproducing information in or from a magnetic recording/reproducing layer or an optical recording/reproducing layer formed on the surface of a discoid substrate made of aluminum, glass, or plastic by a recording/reproducing head such as a magnetic head or an optical pickup.
Disk drives including optical disk drives and magnetic disk units have been frequently used as external memories because personal computers have been spread and advanced in recent years. Therefore, it is requested that these disk drives serving as external memories have a large capacity because computer software has been swollen and the capacity of data to be handled has been increased.
Moreover, a disk drive making the most use of high speed and large capacity is being used not only for computers but also for digital AV units for recording or reproducing images and sounds by employing digital techniques and therefore, a large-capacity disk drive is desired in order to record and reproduce digital AV information including a lot of data. Particularly, a request for increasing the capacity of a high-speed magnetic disk unit has been enhanced more and more because the disk drive is widely applied and positioned as a core.
A conventional magnetic disk unit will be described below.
FIG. 16 is a schematic illustration showing the conventional magnetic disk unit. In FIG. 16, symbol 1 denotes a magnetic disk, 2 denotes a magnetic head for recording or reproducing information in or from the magnetic disk 1, 3 denotes an actuator for having the magnetic head 2 at its front end to perform positioning at an optional radius position of the magnetic disk 1, 5 denotes a head amplifier for detecting and amplifying a reproduced signal of the magnetic head 2, 4 denotes a controller for outputting a control signal for detecting a relative position of the magnetic head 2 to the magnetic disk 1 in accordance with an output of the head amplifier 5 and setting the actuator 3 to a predetermined position on the magnetic disk 1, and 6 denotes a driver for supplying the current corresponding to the control signal to the actuator 3. Moreover, though not illustrated, the following are provided: a spindle motor for rotating the magnetic disk 1, an interface section for transferring digital information to and from a host computer, a buffer and its control section for storing the digital information and efficiently recording or reproducing the information in or from the magnetic disk 1, and a information recording/reproducing circuit.
Then, operations of the conventional magnetic disk unit will be described below. When the magnetic disk 1 records and reproduces information, it is rotated by a not-illustrated spindle motor at a constant speed. In this case, the magnetic head 2 is positioned onto the magnetic disk 1 and held by the actuator 3 while levitated at a position where the pressure of a suspension 3b provided for the front end of the actuator 3 and the working force of the air flow between a slider integrated with a not-illustrated magnetic head 2 and the magnetic disk 1 are balanced. Positional information for detecting the deviation from each of concentric tracks (one track is shown as symbol a by a broken line in FIG. 16), that is, servo information (shown by symbol b in FIG. 16) is previously recorded on each track of the magnetic disk 1. The servo information b is recorded on tracks every certain interval and thereby, the magnetic head 2 reproduces the servo information every certain time in accordance with the rotation of the magnetic disk 1. A region in which the servo information is recorded is referred to as servo region. Thus, information is recorded or reproduced in or from regions other than the servo region and the regions are referred to as data regions.
A reproduced signal of the magnetic head 2 is detected and amplified by the head amplifier 5 and thereby inputted to the controller 4. The controller 4 discriminates servo information in accordance with the inputted signal, computes a positional error to the target track a of the magnetic head 2, moreover computes a controlled variable necessary for driving the actuator 3 so as to reduce the positional error, and outputs a control signal. In this case, a control system for phase compensation or the like is used. The driver 6 supplies a necessary current to a driving coil 3c of the actuator 3 in accordance with an inputted control signal. Thereby a driving force is generated by the driving coil 3c and a permanent magnet 3d set so as to face the coil 3c and the actuator rotates centering around a point c to always position the magnetic head 2 on the target track a. Under the above state, information is recorded or reproduced in or from the data region by the magnetic head 2. Therefore, a positioning control system of a closed loop for positioning a magnetic head on a target track is adopted to record or reproduce information.
However, the above configuration causes the following problems.
That is, to increase the capacity of a magnetic disk unit, it is necessary to increase the information volume which can be recorded in one track, that is, to improve the track recording density or to form tracks in one magnetic disk as many as possible, that is, to improve the track density. In this case, when the track density is improved, in other words, when the distance between adjacent tracks (that is, decreasing the track pitch) is decreased, it is impossible to correctly record or reproduce information unless pieces of the information in adjacent tracks are prevented from interfering each other when recording or reproducing the information. Therefore, it is necessary to improve the positioning accuracy of the target track of a magnetic head and to expand the control bandwidthwidth of the positioning control system.
In case of the conventional method, expansion of a control bandwidthwidth, that is, expansion of the cutoff frequency of an open-loop transfer function is restricted due to the vibration mode resonant frequency of bend or twist of the arm section 3a, suspension 3b, or driving coil 3c of an actuator. FIG. 17(a) shows the frequency-response characteristic of the actuator and FIG. 17(b) shows an open-loop transfer function when applying phase compensation to the controller 4. As shown in FIG. 17(b), because a phase delay occurs due to resonance nearby 2 kHz of the actuator, a control bandwidthwidth is up to 400 Hz. Actually, it was possible to increase the control bandwidthwidth only up to ⅕ to {fraction (1/15)} with respect to the resonant frequency of the vibration mode of the actuator because the control bandwidthwidth must be set to a value lower than 400 Hz by considering dispersion and fluctuation. Therefore, improvement of the positioning accuracy of a magnetic head was limited and resultantly, it was difficult to increase the capacity of a disk drive.
The present invention is made to solve the above problems and its object is to provide an information recording/reproducing apparatus, and method including a magnetic desk unit, which makes it possible to increase the capacity of a disk drive by improving the positioning accuracy of a magnetic head.
An apparatus, and method of the present invention comprises an information recording/reproducing medium, a head for recording or reproducing information while moving relatively to the information recording/reproducing medium, an actuator for supporting the head and movable in accordance with a command, and a control section for controlling movement by supplying a command to the actuator in accordance with a signal reproduced by the head, in which the actuator has at least one vibration mode in addition to the movement mode as a rigid body, the control section is configured by an internal model including at least one vibration mode of the actuator, and a state estimating section for estimating the quantities of states of vibration mode and rigid-body mode of the actuator in accordance with a reproduced signal of the head and a controlled variable corresponding to a movement command to the actuator and a controlled-variable generating section for generating a controlled variable in accordance with each estimated quantity of state estimated by the state estimating section are included.